Glow discharge vacuum pump apparatus



May 7, 1963 R. ZAPHIROPOULOS ETAL GLOW DISCHARGE VACUUM PUMP APPARATUS Filed March 23, 1959 JNVENTORS Re np Zaphiropoulos William A. Lloyd 6 M Attorney Fig.3

United States Patent 3,088,657 GLOW DISCHARGE VACUUM PUMP AlPARATUS Rcnn Zaphiropoulos and William A. Lloyd, Los Altos, Cahf., assiguors to Varian Associates, laio Alto, (Ialif, a corporation of California Filed Mar. 23, 1959, Ser. No. 801,186 Claims. (Cl. 230-69) The present invention relates in general to glow discharge electrical vacuum pump apparatus and more specifically to a novel improved pump configuration which is easier to build and has enhanced operating perform ance. Such glow discharge electrical vacuum pumps utilize the glow discharge principle for sputtering reactive cathode material onto surfaces where it serves to getter gases. This type of vacuum pump is extremely useful in providing very clean high vacuums such as vacuums preferred in electronic tubes, linear accelerators, electron microscopes and many other types of evacuated devices.

Heretofore electrical vacuum pumps of the glow discharge type have been constructed which were relatively difiicult to manufacture and therefore costly due to the many machining operations and different brazes that had to be made during the construction of the pump.

Another disadvantage of the prior art pump is that it was considered at least desirable that the entire inside surface of the metallic pump envelope be covered by an inner liner of reactive cathode material to prevent unwanted sputtering of the envelope material. These liners were mechanically locked in position along the inside of the pump envelope and had the undesired tendency to trap gas between the liner and the envelope in addition to being difiicult to manufacture because of the number of fits that had to be made therebetween.

Another difliculty encountered with the prior art vacuum pump was that although the high voltage anode to cathode insulator was shielded by a shielding member, it was found that after a number of hours of operation, in spite of the shielding, reactive cathode material was being deposited over the insulator to produce undesired current leakage thereacross and voltage breakdown thereof thus deleteriously affecting the operating performance of the pump.

The principal object of the present invention is to provide a novel improved electrical vacuum pump utilizing the glow discharge principle for sputtering reactive cathode material to getter the gas within the pump and said pump including novel features which eliminate the above mentioned prior art difficulties.

One feature of the present invention is the provision of novel cathode plate spacers, said spacers having ears struck therefrom to assure proper cathode plate spacing and provided with a central aperture therein to permit gas access therethrough, whereby the construction of the vacuum pump is greatly simplified and the cost thereof substantially reduced.

Another feature of the present invention is the provision of a novel high voltage insulator assembly, said insulator having a central bore therein closely spaced to an anode support rod passing therethrough whereby mechanical support for the rod is obtained from the insulator, and said insulator further including a reentrant portion spaced apart a greater distance from the anode support rod whereby the current leakage path for the insulator is substantially increased thereby reduc ing the tendency for undesired current leakage and voltage breakdown thereof, in use.

Other features and advantages of the present invention will become apparent upon a perusal of the specification taken in connection with the accompanying drawings wherein,

FIG. 1 is a schematic block diagram depicting a typical evacuation system utilizing the novel vacuum pump of the present invention,

P16. 2 is a plan view partly broken away of a novel electrical vacuum pump apparatus of the present invention,

FIG. 3 is a cross sectional View of the structure of FIG. 2 taken along line 3-3 in the direction of the arrows,

MG. 4 is an elevational view of a cathode separator, and

FIG. 5 is an enlarged cross sectional view of a portion of the structure of FIG. 3 delineated by line 5-5.

Referring now to FIG. 1 there is shown in schematic block diagram form the novel electrical vacuum pump of the present invention as utilized for evacuating a given structure. More specifically, an electrical vacuum pump 1 is connected via a hollow conduit 2 to a compression port 3 and thence via a hollow conduit 4 to the structure 5, which it is desired to evacuate. The compression port 3 serves to provide a valve mechanism whereby the structure 5 and associated conduit 4 may be removed and replaced by another structure and conduit for successive evacuation of a plurality of structures 5. A mechanical vane vacuum pump 6 is also connected to the compression port 3 via conduit 7 and pinch-off valve 8. To evacuate the structure 5, the mechanical vane pump 6 is put into operation serving to reduce the pressure within the structure 5 to a starting pressure less than 20 microns at which point the valve 8 is closed and the electrical vacuum pump .1 started.

Pump 1 is supplied with operating potentials from a source as, for example, a 60 cycle power line via transformer 11. The secondary of transformer 11 is provided with a rectifier 12. and shunting smoothing capacitor 13 whereby a DC. potential may be applied between anode and cathode members of the electrical vacuum pump 1, which will be more fully described below. Although a preferred embodiment utilizes a DC. potential, A.C. potentials are also operable.

Referring now to FIGS. 2 and 3 a shallow rectangular cup shaped member 14- as of, for example, non-magnetic stainless steel, is closed off at its flanged open end by a rectangular closure plate 15, as of non-magnetic stainless steel, welded about its periphery to the flanged portion of member 14 thereby forming a shallow substantially rectangular vacuum tight pump housing 16.

A rectangular cellular anode 17 as of, for example, titanium is carried upon the end of a conductive anode support rod 18 as of, for example, nickel plated nonmagnetic stainless steel which extends outwardly of the rectangular pump housing 16 through an aperture in a short side wall thereof. The anode support rod 18 is insulated from and carried by the pump housing 16 through the intermediaries of a hollow cylindrical adaptor 19, as of nickel plated non-magnetic stainless steel; annular insulator frames 21 and 22 as of, for example, Kovar; and cylindrical insulator 23' as of, for example, glazed alumina ceramic. The free end of the anode support rod 18 serves to provide a terminal for applying a positive anode voltage with respect to two cathode plates 24.

The anode 17 and cathode plates 24, in a preferred embodiment of the present invention, are made of materials having substantially the same coefficient of thermal expansion to prevent flaking of condensed cathode material from the anode surfaces. In a further preferred embodiment the anode 17 and cathode plates 24 are made of substantially the same material whereby a further enhancement in bonding between the condensed cathode material and the condensing anode surface 17 is obtained which further diminishes the tendency for the condensed cathode material to flake off. The flaking off of condensed cathode material is undesired as the flakes may produce an electrical short between the anode 17 and cathode 24, thereby rendering the pump inoperative.

The anode to cathode insulator 23 is provided with a central bore for receiving .therethrough the anode support rod 18. The diameter of the bore is made slightly larger as by, for example, 0.005"-0.0l3" than the outside diameter, as of 0.245", of theanode support rod 18 such that the rod 18 does not make contact at all points about its periphery with the insulator 23; In this manner if contact is made .at all between the rod 18 and the inner bore of the insulator 23, contact is confined to a small area of the rod 18. Thus theefiective current leakage path of the insulator 23 is substantially increased while lending physicalv strength to the overall insulator assembly. In addition, the anode support rod 18 is provided with an undercut portion at 18 to further limit the point of physical contact between anode supportrod 18 and the insulator 23 to a portion of the insulator 23 further removed from the anode 17. The undercut portion 18 of anode support rod 18 extends approximately 0.5" lengthwise of the rod adjacent the inwardly projecting portion of the insulator 23. Thus the inside current leakage path across the insulator has a minimum length of approximately 1 inch, and then one end of the current leakage path is confined to an extremely small area of contact between the rod 18 and the insulator 23. In this manner the typical leakage path is substantially lengthened over a non undercut insulator assembly. Furthermore, the undercut insulator assembly provides a self-shielding feature in that it is extremely difiicult for sputtered cathode material to be condensed on the inside Wall of the centrally. bored insulator 23 adjacent the closely spaced undercut portion 13' of the anode support rod 18.

The two cathode plates 24 are made of a reactive metal and are mechanically locked in position against the large flat side walls of the pump housing 16 via the intermediary of four cathode spacer plates 25, The cathode plates 24 maybe made of any one of a number of reactive cathode metals which may be readily sputtered such as, for example, titanium, chromium, zirconium, gadolinium, and iron.

The cathode spacer plates 25 as of, for example, nonmagnetic stainless steel, are provided with semi-cylindrical cars 26 struck therefrom for assuring the desired spacing between the cathode plates 24 as, for example, 1.5. The cathode plates 24 obtain their proper spacing by riding in bearing engagement upon the ends of the semi-cylindrical ears 26 of the four cathode spacer plates 25 disposed against the four side walls of the pump housing 16 and are held in position thereagainst by the cathode plates 24. The cathode spacer plates 25 are provided with central apertures 20 which thereby minimize the tendency for the cathode spacer plates 25 to trap gases in spaces between the spacer plates 25 and the interior wall of the housing 16. The central apertures 20 further permit free access of gas therethrough when a cathode spacer plate 25 is disposed adjacent the exhaust tubulation 2. The apertures 20 further accommodate the anode support rod 18 which protrudes through one of the cathode spacer plates 25. Thus by providing a central aperture 20 in the cathode spacer plates 25, all four of the cathode spacer plates may be made identical thereby reducing the number of separate parts required.

Another side wall of the vacuum envelope 16 is aper tured to receive the hollow conduit 2, which may be of any convenient inside diameter commensurate with the desired pumping speed. The hollow conduit 2 communicates with the structure which it is desired to evacuate and is provided with a suitable mounting flange.

An annular sputter shield 27 as of, for example, nickel plated non-magnetic stainless steel is carried transversely of conductive rod 18 and is disposed inside the cylindrical adaptor 19 for shielding the insulator 23 from sputtered cathode material which might otherwise coat the insulator 23 and produce unwanted voltage breakdown or current leakage thereacross. The annular sputter shield 27 is closely spaced at its periphery to the cylindrical adaptor 19 as by, for example, to ,4

An annular electrical conducting helical spring 28 is positioned circumscribing the recessed insulator frame member 21 to provide a quick disconnect electrical connection between the power connector, not shown, and the pump housing 16.

A horseshoe shaped permanent magnet 29 is positioned with respect to the shallow rectangular pump housing 16 such that the magnetic field B as of, for example, 850 gauss threads through the individual cellular compartments of the anode 17 in substantial parallelism to the longitudinal axes thereof. The strength of the magnetic field B is preferably related to the characteristic transverse dimension or diameter d of the individual cellular anode compartments approximately in accordance with the following relation:

Although a DC. magnetic field is utilized in a preferred embodiment of the present invention, A.C. magnetic or time varying -D.C. magnetic fields may be utilized. For example, the fringing time varying magnetic field of a circular particle accelerating machine such as the bevatron may be used.

In operation, a positive potential of 0.5 kv. or more is applied to the anode 17 via anode support rod 18. The pump housing 16 and therefore the cathode plates 24 are preferably operated at ground potential to reduce the high voltage hazard to operating personnel; With these potentials applied a region of intense electric field is produced between the cellular anode 17 and the cathode plates 24. This electric field produces a breakdown of gas within the pump resulting in a glow discharge within the cellular anode 17 and between the anode 17 and the cathode plates 24. The glow discharge results in positive ions being driven into the cathode plates 24 to produce dislodgment of reactive cathode material which is thereby sputtered onto the nearby anode 17 to produce'gettering of molecules in the gaseous state coming in contact therewith. In this manner the pressure within the pump housing 16 is reduced, and therefore structures communicating therewith are evacuated.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted .as illustrative and not in a limiting sense.

What is claimed is:

1. A glow discharge electrical vacuum pump apparatus including; a shallow flanged open ended cup-shaped housing member having short side walls; a cover member closing said housing member and being sealed at its periphery in a gas tight manner to said housing member; means forming an entrance into said-housing, member for gaseous fluid to be pumped; a reactive cathode member having one portion disposed adjacent the bottom Wall of said cup-shaped housing member and a second portion disposed adjacent said cover member; a cathode spacer member carried within said cup-shaped housing member and disposed adjacent the short side walls thereof, said cathode spacer having ears struck therefrom for engaging said cathode portions to assure proper spacing therebetween; an anode member disposed between said first and second cathode portions and spaced apart therefrom; a high voltage insulator assembly for allowing operating potentials to be applied to said anode and cathode members to produce sputtering of said reactive cathode member and including, .a longitudinal bored vacuum sealed insulator, an anode support rod coaXi-ally disposed within said insulator bore, the inside diameter of said insulator bore being slightly larger than the outside diameter of said support rod for a first portion of said insulator bore, and a second portion of said insulator bore being spaced apart a slightly larger distance from said anode support rod whereby the current leakage path of said insulator assembly is substantially increased.

2. A glow discharge electrical vacuum pump apparatus including, a reactive cathode member having at least two spaced apart portions, an anode member disposed between and spaced apart from the two portions of said cathode member, a vacuum tight pump housing enveloping said anode and cathode members, means forming an entrance into said housing for gaseous fluid to be pumped, and a cathode spacer member having a plurality of ears struck therefrom for engaging the two spaced apart cathode pontions to assure the proper spacing therebetween.

3. The apparatus according to claim 2 wherein said ears have a semi-cylindrical shape.

4. The apparatus according to claim 2 wherein said cathode spacer member is apertured for gas access therethrough.

5. The apparatus according to claim 3 wherein said cathode spacer member is a substantially rectangular plate having a centrally disposed aperture therein for gas access therethrough.

6. A glow discharge electrical apparatus including; a cathode member having at least two spaced apart portions; an anode member disposed between and spaced apart from the two spaced portions of said cathode member; a vacuum tight housing enveloping said anode and cathode members; means forming an entrance into said housing for gaseous fluid to be pumped; means for applying different operating potentials to said anode and cathode members to establish a glow discharge therebetween in use; an electrically conducting anode support rod mechanically supporting and connected to said anode within said housing; and an insulator assembly for vacuum sealing said anode support rod to said housing; said insulator assembly including, a longitudinally bored vacuum sealed insulator having said anode support rod coaxially disposed within said insulator bore, the inside diameter of said insulator bore being slightly larger than the outside diameter of said support rod for a first portion of said insulator bore, and a second portion of said insulator bore being spaced apart a slightly larger distance from said anode support rod for substantially increasing the current leakage path of said insulator assembly.

7. The apparatus according to claim 6 including, means for vacuum sealing said insulator to said housing at the outside periphery of said insulator and intermediate the length thereof thereby providing a re-entrant longitudinal portion of said insulator protruding within said vacuum tight housing.

8. The apparatus according to claim 7 wherein said reentrant longitudinally protruding portion of said insulator comprises substantially said second portion of said insulator bore whereby the current leakage path of said insulator is substantially increased.

9. The apparatus according to claim 8 including, a transversely extending sputter shield member carried from said anode support rod and being closely spaced to said reentrant portion of said insulator for preventing sputtered cathode material from coating the surface of said insulator within said housing.

10. The apparatus according to claim 6 wherein said vacuum tight housing is circumferentially recessed in close proximity to said insulator assembly; and a conductive helical spring carried within said recessed portion of said housing for facilitating electrical contact with said housmg.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A GLOW DISCHARGE ELECTRICAL VACUUM PUMP APPARATUS INCLUDING; A SHALLOW FLANGED OPEN ENDED CUP-SHAPED HOUSING MEMBER HAVING SHORT WALLS; A COVER MEMBER CLOSING AND HOUSING MEMBER AND BEINB SEALED AT ITS PERIPHERY IN A GAS TIGHT MANNER TO SAID HOUSING MEMBER; MEANS FORMING AN ENTRANCE INTO SAID HOUSING MEMBER FOR GASEOUS FLUID TO BE PUMPED; A REACTIVE CATHODE MEMBER HAVING ONE PORTION DISPOSED ADJACENT THE BOTTOM WALL OF SAID CUP-SHAPED HOUSING MEMBER AND A SECOND PORTION DISPOSED ADJACENT SAID COVER MEMBER; A CATHODE SPACER MEMBER CARRIED WITHIN SAID CUP-SHAPED HOUSING MEMBER AND DISPOSED ADJACENT THE SHORT SIDE WALLS THEREOF, SAID CATHODE SPACER HAVING EARS STRUCK THEREFROM FOR ENGAGING SAID CATHODE PORTIONS TO ASSURE PROPER SPACING THEREBETWEEN; AN ANODE MEMBER DISPOSED BETWEEN SAID FIRST AND SECOND CATHODE PORTIONS AND SPACED APART THEREFROM; A HIGH VOLTAGE INSULATOR ASSEMBLY FOR ALLOWING OPERATING POTENTIALS TO BE APPLIED TO SAID ANODE AND CATHODE MEMBERS TO PRODUCE SPUTTERING OF SAID REACTIVE CATHODE MEMBER AND INCLUDING, A LONGITUDINAL BORED VACUUM SEALED INSULATOR, AN ANODE SUPPORT ROD COAXIALLY DISPOSED WITHIN SAID INSULATOR BORE, THE INSIDE DIAMETER OF SAID INSULATOR BORE BEING SLIGHTLY LARGER THAN THE OUTSIDE DIAMETER OF SAID SUPPORT ROD FOR A FIRST PORTION OF SAID INSULATOR BORE, AND A SECOND PORTION OF SAID INSULATOR BORE BEING SPACED APART A SLIGHTLY LARGER DISTANCE FROM SAID ANODE SUPPORT ROD WHEREBY THE CURRENT LEAKAGE PATH OF SAID INSULATOR ASSEMBLY IS SUBSTANTIALLY INCREASED. 